The present invention relates to an electroluminescent device (hereinafter referred to as xe2x80x9cEL devicexe2x80x9d) and a method for the production of the same. In particular, the present invention relates to an EL device which can be produced and stored in the form of a roll as a stock product having a luminescent layer which continuously extends in the lengthwise direction of the roll-form device, unlike conventional EL devices produced by screen printing, and a method for the production of the same.
Luminescent layers and other layers of conventional EL devices are formed by silk-screen printing, as disclosed in JP-B-59-14878, JP-B-62-59879, etc. Thus, the size of the EL devices is limited by the size of a printing plate, and it is difficult to produce an EL device having a luminescent layer with a large area or which continuously extend in the lengthwise direction of the device. Also it is impossible to produce a roll-form EL device having a luminescent layer continuously extending in the lengthwise direction as a stock product.
When a stock product of an EL device having a continuous luminescent layer in the lengthwise direction can be produced and stored, an EL device having a required length can be obtained by cutting the stock product in a required length on demand, and the EL devices can be easily applied to various products. Thus, it is strongly desired to provide such a roll-form EL device.
Conventional EL devices are suitable for luminescent displays having a small plane size (small area) such as watches, pagers (beepers), portable phones, notebook-size personal computers, handy terminals, etc. but they cannot be used to assemble large-sized luminescent displays such as billboards, signs,. plane illuminators (e.g. floor illuminators, etc.), and the like.
If large-sized luminescence displays are assembled using conventional EL devices, a number of EL devices should be connected with each other, and thus, productions and construction of such displays are extremely difficult.
It is also important to increase the luminance of EL devices for the realization of large-sized luminescent displays. For example, the above cited patent publications disclose EL devices having a so-called xe2x80x9cdispersion type luminescent layerxe2x80x9d which is formed by dispersing luminescent particles such as fluorescent particles in matrix resins such as polymers having a high dielectric constant. For example, JP-B-S9-14878 discloses an EL device comprising a transparent substrate, a transparent conductive layer, an insulating layer consisting of a vinylidene fluoride polymer as a matrix resin, a fluorescent layer comprising fluorescent particles and a vinylidene fluoride polymer as a matrix resin, the same insulating layer as above, and a rear electrode, which are laminated in this order. JP-B-S9879 discloses an EL device comprising a polyester film, an ITO electrode, a luminescent layer comprising fluorescent particles and a cyanoethylated ethylene-vinyl alcohol copolymer (a matrix resin), and an aluminum foil (a rear electrode), which are laminated in this order. In these EL devices, a luminescent layer is formed by the application of a coating containing luminescent particles dispersed in a matrix resin. Thus, the luminance of the device can be increased by the increase of the amount of luminescent particles in the coating. However, the increase of the amount of the luminescent particles to an unnecessary level may make it difficult to apply the coating continuously at a high rate.
U.S. Pat. Nos. 5,019,748 and 5,045,755 disclose an EL device having a luminescent layer which is formed from (1) a first dielectric adhesive layer having a high dielectric constant applied on the transparent conductive layer of a transparent substrate, (2) a fluorescent particle layer in the form of a substantially single layer (having a thickness not exceeding the largest size of particles), which is formed by applying dry fluorescent particles (luminescent particles) on the first dielectric adhesive layer, and (3) a second dielectric layer containing a filler having a high dielectric constant. In contrast with the above xe2x80x9cdispersion type luminescent layerxe2x80x9d, it is easy to continuously carry out the coating processes, and it is possible to produce a roll-form EL device by the disclosed method. However, these U.S. patent specifications do not disclose any specific manner to form a continuous terminal (buss), through which an electricity (voltage) is applied from outside to the transparent conductive layer, along the lengthwise direction of the transparent substrate, in the production steps of the roll-form EL device.
Furthermore, to increase the area of EL devices, it is a key factor that how a terminal (buss), which supplies an electricity (a voltage) to a transparent conductive layer from the outside, is provided. For example, in the case of EL devices for the above described displays with a small area, busses, which are not electrically in contact with luminescent layers or rear electrodes, can be formed on a transparent conductive layer by effectively repeating screen printing. However, none of the above cited publications or patents disclose any method to form busses continuously in the lengthwise direction of the device.
On the other hand, in the case of xe2x80x9cdispersion type luminescent layersxe2x80x9d, it is difficult to form luminescent layers with improved luminance continuously at a high rate, that is, at a high productivity. The reason for this is that luminescent particles, which have a larger specific gravity than matrix resins, tend to sink in a coating for forming luminescent layers comprising luminescent particles dispersed in the solution of matrix resins, and thus it is difficult to uniformly disperse the luminescent particles in the luminescent layers formed from such a coating.
Furthermore, the dispersibility deteriorates when the amount of luminescent particles in the coating is increased to increase the filling rate of luminescent particles in the luminescent layer. The filling rate of the luminescent particles is at most 20 vol. % of the whole luminescent layer. In addition, it is relatively difficult to increase the coating thickness of the luminescent layer while maintaining the uniformity of a thickness using such a dispersion type coating. Therefore, the number of applications of the coating should be increased to increase the thickness of the luminescent layer for increasing the luminance, the productivity decreases, and it is difficult to produce a roll-form EL device having a large area.
There is a great need for an EL device which can be formed in the form of a roll, and from which large-sized luminescent displays can be easily produced, in order to solve the problems associated with the above-described prior arts. There is also a need for an EL device which can easily increase a filling rate the luminescent particles in a luminescent layer and thus improve the luminance of the device, in addition to the easy formation of large-sized luminescent displays. Also, there is a need for a roll-form EL device having a high luminance and a large area, which can be produced at a high productivity using no dispersion coating containing luminescent particles.
In one embodiment, the present invention provides an electroluminescent device having a transparent substrate which extends in the lengthwise direction of the device; a transparent conductive layer placed on the back surface of the transparent substrate; a luminescent layer having a width which is smaller than the width of the transparent conductive layer and being placed on the back surface of the transparent conductive layer; a rear electrode placed on the back surface of the luminescent layer; and at least one buss which is placed on the part of the back surface of the transparent conductive layer having no luminescent layer, has a width smaller than the width of the transparent conductive layer, and is electrically in contact with neither the luminescent layer nor the rear electrode wherein the transparent conductive layer, the luminescent layer, the rear electrode and the buss continuously extend in the lengthwise direction of the transparent substrate.
In another embodiment, the present invention provides a method for producing an electroluminescent device including the steps of providing a transparent substrate on one surface of which a transparent conductive layer is applied; placing the luminescent layer on the transparent conductive layer by a coating process so that the width of the luminescent layer is smaller than that of the transparent conductive layer to form a luminescent layer carrying substrate; placing a masking on an exposed part of the transparent conductive layer of the luminescent layer-carrying substrate, which part has no luminescent layer, in the lengthwise direction of the transparent substrate, where the masking has a width smaller than that of the exposed part carrying no luminescent layer; and applying a conductive material onto the luminescent layer-carrying substrate to form the rear electrode and the buss which is electrically in contact with neither the luminescent layer nor the rear electrode due to the presence of the masking or the exposed part from which the masking is removed.
In another embodiment, the present invention provides a method for producing an electroluminescent device including the steps of: providing a transparent substrate on one surface of which a transparent conductive layer is applied; placing a masking on the surface of the transparent conductive layer to cover a buss-forming area, on which the buss is formed, with the masking, so that a buss-forming area having the applied masking and a masking-free area having no masking are formed on the transparent conductive layer; placing the luminescent layer on the masking-free area of the transparent conductive layer by a coating process to form a luminescent layer-carrying substrate; applying a conductive material onto the luminescent layer-carrying substrate to form the rear electrode on the luminescent layer; removing at least a part of the masking to expose the buss-forming area; and then applying a conductive material onto the exposed buss-forming area, to form the rear electrode and the buss which is electrically in contact with neither the luminescent layer nor the rear electrode due to the presence of the masking or the exposed part from which the masking is removed.
Furthermore, in another embodiment, the present invention provides an electroluminescent device, in which the luminescent layer includes: a transparent support layer comprising a matrix resin and being placed on the side of the transparent conductive layer; an insulating layer comprising an insulating material and being placed on the side of the rear electrode; and a luminescent particle layer having luminescent particle which are embedded in both the support layer and the insulating layer.